Russia is the birthplace of a group of athletes who have affected the World Tennis Association rankings in the same way that zebra mussels have affected the Great Lakes — which is to say, pretty much clogged them. The invasion happened swiftly: at the end of 2001, Russia had one woman (Elena Dementieva) in the W.T.A. Tour’s top 30. By the start of 2007, Russian women accounted for fully half of the top 10 (Dementieva, Maria Sharapova, Svetlana Kuznetzova, Nadia Petrova and Dinara Safina) and 12 of the top 50. Not to mention 15-year-old Anastasia Pavlyuchenkova, who was the International Tennis Federation’s No. 1-ranked junior and who was joined in the top 500 by five countrywomen also named Anastasia.